llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-clang
Author: Gábor Spaits (spaits)
<details>
<summary>Changes</summary>
This PR would solve issue #<!-- -->62925.
The following code:
```cpp
#include <map>
int main() {
std::map m1 = {std::pair{"foo", 2}, {"bar", 3}}; // guide #<!-- -->2
std::map m2(m1.begin(), m1.end()); // guide #<!-- -->1
}
```
Is rejected by clang, but accepted by both gcc and msvc:
https://godbolt.org/z/6v4fvabb5 .
So basically CTAD with copy-list-initialization is rejected.
Note that this exact code is also used in a cppreference article:
https://en.cppreference.com/w/cpp/container/map/deduction_guides
I did some debugging and found out, that the reason why this does not work in
clang is that, in the function
`Sema::DeduceTemplateSpecializationFromInitializer` we explicitly suppress user
conversion, if the initialization type is a copy initialization.
I checked the C++11 and C++20 standard drafts to see whether suppressing user
conversion is the correct thing to do for user conversions. Based on the
standard I don't think that it is correct.
```
13.3.1.4 Copy-initialization of class by user-defined conversion
[over.match.copy]
Under the conditions specified in 8.5, as part of a copy-initialization of an
object of class type, a user-defined
conversion can be invoked to convert an initializer expression to the type of
the object being initialized.
Overload resolution is used to select the user-defined conversion to be invoked
```
So we could use user defined conversions according to the standard.
```
If a narrowing conversion is required to initialize any of the elements, the
program is ill-formed.
```
We should not do narrowing.
```
In copy-list-initialization, if an explicit constructor is chosen, the
initialization is ill-formed.
```
We should not use explicit constructors.
Also a note:
In `InitializationKind::InitKind` there is no init kind called `IK_CopyList`
but there is `IK_DirectList`, should we add `IK_CopyList`? Or it is unnecessary
for now?
---
Full diff: https://github.com/llvm/llvm-project/pull/94752.diff
3 Files Affected:
- (modified) clang/include/clang/Sema/Initialization.h (+1-1)
- (modified) clang/lib/Sema/SemaInit.cpp (+2-4)
- (added) clang/test/SemaCXX/ctad-copy-init-list-narrowing.cpp (+90)
``````````diff
diff --git a/clang/include/clang/Sema/Initialization.h
b/clang/include/clang/Sema/Initialization.h
index f443e327eaf32..4b876db436b48 100644
--- a/clang/include/clang/Sema/Initialization.h
+++ b/clang/include/clang/Sema/Initialization.h
@@ -603,7 +603,7 @@ class InitializationKind {
/// Normal context
IC_Normal,
- /// Normal context, but allows explicit conversion functionss
+ /// Normal context, but allows explicit conversion functions
IC_ExplicitConvs,
/// Implicit context (value initialization)
diff --git a/clang/lib/Sema/SemaInit.cpp b/clang/lib/Sema/SemaInit.cpp
index ed8b226a6b39f..211b6887befa3 100644
--- a/clang/lib/Sema/SemaInit.cpp
+++ b/clang/lib/Sema/SemaInit.cpp
@@ -10892,8 +10892,6 @@ QualType
Sema::DeduceTemplateSpecializationFromInitializer(
// FIXME: The "second phase of [over.match.list] case can also
// theoretically happen here, but it's not clear whether we can
// ever have a parameter of the right type.
- bool SuppressUserConversions = Kind.isCopyInit();
-
if (TD) {
SmallVector<Expr *, 8> TmpInits;
for (Expr *E : Inits)
@@ -10903,12 +10901,12 @@ QualType
Sema::DeduceTemplateSpecializationFromInitializer(
TmpInits.push_back(E);
AddTemplateOverloadCandidate(
TD, FoundDecl, /*ExplicitArgs=*/nullptr, TmpInits, Candidates,
- SuppressUserConversions,
+ /*SuppressUserConversions=*/false,
/*PartialOverloading=*/false, AllowExplicit, ADLCallKind::NotADL,
/*PO=*/{}, AllowAggregateDeductionCandidate);
} else {
AddOverloadCandidate(GD, FoundDecl, Inits, Candidates,
- SuppressUserConversions,
+ /*SuppressUserConversions=*/false,
/*PartialOverloading=*/false, AllowExplicit);
}
};
diff --git a/clang/test/SemaCXX/ctad-copy-init-list-narrowing.cpp
b/clang/test/SemaCXX/ctad-copy-init-list-narrowing.cpp
new file mode 100644
index 0000000000000..21b1137158d5a
--- /dev/null
+++ b/clang/test/SemaCXX/ctad-copy-init-list-narrowing.cpp
@@ -0,0 +1,90 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -Wno-unused-value -std=c++20 %s
+namespace std
+{
+ typedef long unsigned int size_t;
+}
+
+namespace std
+{
+ template<class _E>
+ class initializer_list
+ {
+ public:
+ typedef _E value_type;
+ typedef const _E& reference;
+ typedef const _E& const_reference;
+ typedef size_t size_type;
+ typedef const _E* iterator;
+ typedef const _E* const_iterator;
+
+ private:
+ iterator _M_array;
+ size_type _M_len;
+
+
+ constexpr initializer_list(const_iterator __a, size_type __l)
+ : _M_array(__a), _M_len(__l) { }
+
+ public:
+ constexpr initializer_list() noexcept
+ : _M_array(0), _M_len(0) { }
+
+
+ constexpr size_type
+ size() const noexcept { return _M_len; }
+
+
+ constexpr const_iterator
+ begin() const noexcept { return _M_array; }
+
+
+ constexpr const_iterator
+ end() const noexcept { return begin() + size(); }
+ };
+
+ template<class _Tp>
+ constexpr const _Tp*
+ begin(initializer_list<_Tp> __ils) noexcept
+ { return __ils.begin(); }
+
+ template<class _Tp>
+ constexpr const _Tp*
+ end(initializer_list<_Tp> __ils) noexcept
+ { return __ils.end(); }
+}
+
+template<class T, class Y>
+class pair{
+ private:
+ T fst;
+ Y snd;
+ public:
+ pair(T f, Y s) : fst(f), snd(s) {}
+};
+
+template<class T, class Y>
+class map {
+ public:
+ map(std::initializer_list<pair<T, Y>>, int a = 4, int b = 5) {}
+};
+
+template<class T, class Y>
+class Contained {
+ public:
+ Contained(T, Y) {}
+};
+
+template<class T, class Y>
+class A {
+ public:
+ A(std::initializer_list<Contained<T, Y> >, int) {}
+};
+
+int main() {
+ map mOk ={pair{5, 'a'}, {6, 'b'}, {7, 'c'}};
+ map mNarrow ={pair{5, 'a'}, {6.0f, 'b'}, {7, 'c'}}; // expected-error
{{type 'float' cannot be narrowed to 'int' in initializer list}} //
expected-note {{insert an explicit cast to silence this issue}}
+
+ A aOk = {{Contained{5, 'c'}, {5, 'c'}}, 5};
+ A aNarrowNested = {{Contained{5, 'c'}, {5.0f, 'c'}}, 5}; // expected-error
{{type 'float' cannot be narrowed to 'int' in initializer list}} //
expected-note {{insert an explicit cast to silence this issue}}
+ A aNarrow = {{Contained{5, 'c'}, {5, 'c'}}, 5.0f}; // expected-error
{{type 'float' cannot be narrowed to 'int' in initializer list}} //
expected-note {{insert an explicit cast to silence this issue}}
+}
``````````
</details>
https://github.com/llvm/llvm-project/pull/94752
_______________________________________________
cfe-commits mailing list
cfe-commits@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
